In a variety of commercial and industrial settings it is necessary to remove one or more substances from a gas before the gas can be used for a particular purpose. For example, before compressed air can be used to drive power tools, any water or water vapor must be removed from the compressed gas or the tools will rust. Likewise, before air contaminated with a toxic or noxious substance can be inhaled, the substance must be removed.
Many types of devices are available to remove one or more substances from a gas. One particularly effective class of devices is known as a pressure swing sorption system. Such a system directs a flow of the gas through a bed of sorbent material. A sorbent material is one which sorbs, i.e., absorbs or adsorbs, certain substances. During a sorption phase, the gas containing the substances, i.e., the inlet gas, is directed at a predetermined pressure through a sorbing chamber which contains the sorbent bed and the substances are sorbed by the sorbent material. As the substances are sorbed by the sorbent material, the heat of absorption heats the sorbent bed and this heat is conserved, as taught in U.S. Pat. No. 2,944,627, one of the most widely recognized patents related to pressure swing adsorbers. Because the substances are sorbed by the sorbent material, the outlet gas is free of the substances or has a much lower concentration of the substances.
To extend the useful life of these sorbing systems, a second sorbing chamber with a second sorbent bed is provided. The inlet gas is then redirected from the first sorbing chamber to the second sorbing chamber where the substance is sorbed by the sorbent material in the second sorbing chamber. The sorbent bed in the first sorbing chamber is then regenerated, i.e., purged or stripped of the substances it previously sorbed from the gas. During the regeneration phase, the first sorbing chamber is typically depressurized and a portion of the outlet gas from the second sorbing chamber is directed back through the first sorbing chamber, purging the substances from the sorbent bed. As taught by U.S. Pat. No. 2,944,627, the heat of adsorption induced in the sorbent bed of the first sorbing chamber during the sorption phase is substantially completely utilized to desorb the substance from the sorbent bed during the regeneration phase. The purge gas, now containing much of the substances previously sorbed by the sorbent bed, is then vented through an exhaust. Once the sorbent bed in the first sorbing chamber is sufficiently free of the substances, the first sorbing chamber may be repressurized and the inlet gas may be redirected through the first sorbing chamber while the second sorbing chamber is regenerated. The pressure swing sorption system can continue cycling between the sorption phase and the regeneration phase of the first and second sorbing chambers for an extended period.
As effective as these systems are, they nevertheless have certain undesirable characteristics. For example, the portion of the outlet gas which must be directed back through a sorbing chamber to regenerate the sorbent bed can be very large. For example, from about 15% to about 67% of the inlet gas may be used as purge gas to regenerate a sorbent bed. Consequently, the amount of output gas which can be used for its intended purpose is greatly reduced.